1. Field of the Invention
The present invention relates to inkjet recording apparatuses and image forming apparatuses. More specifically, the present invention relates to an inkjet recording apparatus that prints on a recording medium (which is hereinafter called a paper sheet) conveyed by a conveyance member such as a conveyor belt by discharging ink from nozzles in an ink discharging head, and an image forming apparatus that utilizes the inkjet recording apparatus.
2. Description of the Related Art
Conventionally, in an inkjet recording apparatus, a so-called “blank discharge” is generally performed to maintain a sufficient ink discharge by always preventing nozzles in an ink discharge head from drying, other than nozzle maintenance performed before starting the next print job. In the blank discharge, the nozzles discharge ink irrelevant to image forming toward an area above a paper sheet being conveyed during printing, a conveyance member between the paper sheets, or a blank discharge ink receiver disposed behind a conveyance unit through a paper sheet suction hole provided in the conveyance member or through an opening provided in the conveyance member only for the blank discharge.
However, it sometimes happens that the blank discharge contaminates a surface of a conveyor belt with the ink because a head nozzle faces the surface of the conveyor belt that is the conveyor member, on a paper sheet supporting side. To prevent such contamination, a technique that displaces the conveyor belt, and carries an ink receiver for the blank discharge into a position where the conveyor belt has existed, is proposed. However, the inkjet recording apparatus in this technique has a complex structure and has grown in size as a whole, and even causes a decrease of printing efficiency because a transfer action for the conveyor belt being displaced and carrying the ink receiver in place of the conveyor belt make a printing interruption time longer.
In Japanese Laid-open Patent Application Publication No. 2007-168277 (which is hereinafter called Patent Document 1), a blank discharge in an inkjet recording apparatus is disclosed. In the blank discharge, a nozzle discharges ink irrelevant to image forming toward a blank discharge ink receiver disposed behind a conveyor belt through a paper sheet suction hole provided in the conveyor belt at a proper timing during printing. In Patent Document 1, corresponding to the blank discharge, the inkjet recording apparatus includes the blank discharge ink receiver that is large enough to be able to receive even spreading blank discharge ink. However, even if the blank discharge ink receiver has such a large size, a small ink droplet, especially misty ink, tends to float up in the air around a blank discharge receiver part, which sometimes causes the ink to overflow outside the ink receiver from a gap between the ink receiver and an opposing face plate. In particular, when a suction unit (e.g., suction fan) for suctioning a paper sheet is provided, the inside of the blank discharge ink receiver is reduced to a negative pressure due to air flow caused by the suction fan, and even a relatively big ink droplet once returned to the blank discharge ink receiver falls out of the gap between the blank discharge ink receiver and the opposing face plate. This sometimes causes not only a decrease of an ink recovery rate, but also an accumulation of contamination by the blank discharge ink around the blank discharge receiver, and diffuse emission of the blank discharge ink outside the inkjet recording apparatus by the paper sheet suction fan.
An explanation is given by using drawings. FIG. 1 is a diagram showing a side of a conventional public blank discharge ink receiver 22. FIG. 1 shows a blank discharge ink recovery mechanism that includes blank discharge ink receivers 22Y through 22K arranged along a recording head line. A paper sheet is suctioned and carried from the left to the right of FIG. 1. In FIG. 1, a part of the blank discharge ink receivers and the recording heads are omitted for reduction of the drawing. The recording heads 18Y through 18K respectively include plural head nozzles arranged in a direction perpendicular to a paper sheet conveyance direction (i.e., a direction perpendicular to the plane of paper of FIG. 1). The blank discharge ink receivers 22Y through 22K have a length capable of accepting an ink droplet flow discharged from the head nozzles for the blank discharge (which is hereinafter called a blank discharge ink flow; refer to FIG. 18).
A suction fan 23 is provided under the blank discharge ink receiver 22 as a paper sheet suction unit, which makes it possible to suction and hold the paper sheet carried onto a surface of a conveyor belt 8 through plural suction holes 8a provided through the conveyor belt 8 and plural suction holes 13a provided through a belt flexure prevention member 13, and to carry the paper sheet.
In a configuration shown in FIG. 1, when a blank discharge ink flow 19 flows into an inside space of the blank discharge ink receiver 22 as shown in FIG. 2, air flows into not only the suction holes 13a provided in the flexure prevention member 13, but also openings 13b for the blank discharge ink provided facing the head nozzles. Here the openings for the blank discharge ink 13b are provided to let the blank discharge ink flow 19 through due to the suction fan 23 of the paper sheet suction unit. Because the air flows along a side piece of the blank discharge ink receiver 22, the inside of the blank discharge ink receiver 22 is reduced to a negative pressure state. Due to this, as shown in FIG. 3, the blank discharge ink flow 19 that first flows into the blank discharge ink receiver 22 does not stay in the inside space of the blank discharge ink receiver 22, and a part of the blank discharge ink flow 19 leaks out from a top edge 22a of the blank discharge ink receiver 22 as an outward ink flow 19a. 